Application Of Gravity Method In Oil And Gas Evaluation And Exploration In Yihe Sag

Gravity exploration is a traditional geophysical exploration method based on the differences in density between rock ores, which conduct the study of the geological problems and the search for mineral resources. Gravitational forward fitting is to fit the measured gravity anomaly by establishing and modifying the initial source model,obtain the field property parameters and geometric parameters, through the forward technology to achieve the purpose of inversion. Gravity information plays an important role in the basin "exploratory bottoming","indentation belt" and so on. Normalized full gradient method of gravity anomalies is a kind of detecting and estimating the position of the gravity anomaly field source body method by using gravitational field of the feature points or the analytic function of singularity. In this paper, normalized full gradient method is studied by the horizontal cylinder and their the combination model and the anticline structure of the three-dimensional body, and the oil gas pool (or low density body) at the top of the anticlinal structure is detected by the characteristics of the "two-high clamp low" of Normalized full gradient field in the vertical plane of lead.The Erlian basin is composed of many small sag, Yihe sag is one of them. During the formation of sag, sandstone and mudstone will be separated. However, the separation degree of sand and mudstone determines whether sag is good or not (the degree of finding oil), the better the degree of separation, the better prospects of oil.Among them, the transport distance and hydrodynamic active degree are the decisive factors that determine the degree of sand and mud separation. The main exploration stratum of the Yihe sag is the Lower Cretaceous Bayanian, and the main oil-bearing strata are Paleozoic strata, Arshang Group and one section of Tengger Group.This paper deeply analyzes the basic principle of the normalized total gravity gradient method combined with theory model,and applied it to sag. The results show that the depression rating is good. The forward modeling of the two lines is visualized by using 2.5D modeling positive inversion techniques,in which the two lines across the main subsags. Among them,the geometric parameters of the initial model are taken from the two-dimensional seismic interpretation results. The longitudinal density in the physical parameters is derived from the acoustic wave velocity data. The lateral variation of density is achieved by human-computer interaction test and error adjustment.The results of forward modeling revealed that there was a large of density heterogeneity in the lateral and longitudinal direction of the main subsags,and the main subsags is favorable for oil and gas generation. Compared with the results of seismic interpretation, the depth difference of them in the Saihan Group-Quaternary and Tengger Group is not significant, but the results of the bottom fitting are different from those of the seismic interpretation. Through the drilling results verify, The depth of each sedimentary layer by forward modeling is consistent with the depth of each layer revealed by the drilling, and confirmed that the existence of coarse-fime-coarse sedimentary cycles (Yihe group) in the bottom of the A'ershan Group from the perspective of geometric and physical properties (density) is reasonable. However,the results of the two-dimensional seismic interpretation are shallow and its possible causes is that the speed of the early time-depth conversion is too small or there are error layers on the early seismic interpretation.